1. Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device having electrodes which provide electron emission from electron emission regions with enhanced equipotential patterns.
2. Description of Related Art
Among the known types of the electron emission devices having cold cathodes as the electron emission sources are the field emitter array (FEA) type, the surface conduction emitter (SCE) type, and the metal-insulator-metal (MIM) type.
The FEA type is based on the principle that when a material with a lower work function or a higher aspect ratio is used to form the electron emission source, electrons are easily emitted therefrom by the application of an electric field under a vacuum atmosphere.
A tapered tip structure based on with molybdenum (Mo) or silicon (Si), can be used in forming the electron emission source. With the tip structure, it has an advantage of making it easy to emit electrons therefrom, since the electric field is focused on the sharp front end thereof. However, such a structure is made through a semiconductor process such that the relevant processing steps are complicated, and as the device becomes large, it is difficult to make the device have uniform quality.
On the other hand, carbon-based material, such as carbon nanotube, graphite and diamond-like carbon can be used in forming the electron emission source. In this regard, efforts have been recently made to replace the tip structure with a carbon-based material. Particularly, the carbon nanotube is expected to be an ideal electron emission material since it involves an extremely small end curvature radius of 100 angstroms, and emits electrons well even under a low electric field of 1-10V/μm. With regard to the electron emission device using the carbon nanotube, U.S. Pat. Nos. 6,062,931 and 6,097,138 disclose a cold cathode field emission display.
The FEA type electron emission display may be formed with a triode structure having cathode, gate and anode electrodes. Cathode electrodes, an insulating layer and gate electrodes are sequentially formed on a first substrate, and openings are formed at the gate electrodes and the insulating layer, followed by forming electron emission regions on the portions of the cathode electrodes exposed through the openings. An anode electrode and phosphor layers are formed on the second substrate.
With the above FEA structure, when predetermined driving voltages are applied to the cathode and the gate electrodes, and a positive (+) voltage of several hundreds to several thousands volts is applied to the anode electrode, electric fields are formed around the electron emission regions due to the potential difference between the cathode and the gate electrodes so that electrons are emitted from the electron emission regions. The emitted electrons are attracted by the higher voltage applied to the anode electrode, and collide against the relevant phosphors, thereby exciting them.
However, with the above-structured FEA electron emission device, without any electrode for focusing the electron beams around the electron emission region, the electrons emitted from the electron emission region are diffused at an inclination when they proceed toward the second substrate. Accordingly, the electrons emitted from the electron emission region at the specific pixel do not land on the correct phosphor but strike the neighboring incorrect phosphors. Such a deviation from the designated path causes deterioration in the color purity of the screen and the readability.
Further, with the above-described FEA structure, the emission characteristic of the electron emission regions per the respective pixels is not uniform so that the inter-pixel brightness characteristic becomes uneven. The non-uniformity in the emission characteristic may be due to various factors. Among them, on the one hand, the patterning precision of the electron emission regions is not excellent so that the electron emission regions are differentiated in shape per the respective pixels, and on the other, the device is of large-size so that a voltage drop is made due the internal resistance of the electrodes.
Given this situation, it has been proposed that a focusing electrode should be formed on the gate electrode, and a resistance layer located between the cathode electrode and the electron emission region, thereby achieving the focusing of the electron beams and the uniformity of the emission characteristic per the respective pixels. However, as the above structure is provided with the resistance layer and the focusing electrode in a separate manner, the relevant processing steps become complicated and increase production cost. In particular, when the focusing electrode is formed on the gate electrode, openings for exposing the electron emission regions need to be formed at the focusing electrode, and these openings necessitate complicated processing steps which make it difficult to form the electron emission regions.